In a typical rotor assembly of an axial flow turbine, a plurality of rotor blades extend outwardly from a disk, or drum shaped structure. The blades extend across an annular flowpath for working medium, and in turbine embodiments extract energy from the working medium gases flowing across the blades. Each of the blades is formed of an airfoil section extending into the flowpath, a root section interlockingly engaging the disk or drum, and a platform section defining the inner boundary of the working medium flowpath.
The sequence of rotor blades passing through local aerodynamic perturbations in the working medium flowpath initiate alternatingly increased and decreased loadings on the blades. This variation in loading characteristic induces blade deflection and imparts a stress on the blade material. If the frequency at which the loading characteristic varies is coincident with the natural frequency of the blade resonance occurs; the deflection amplitudes become reinforcing and vibratory damage likely results.
Vibratory phenomenon and the need to attend to such problems in rotary machines has long been recognized. U.S. Pat. Nos. 3,112,915 to Morris entitled "Rotor Assembly Air Baffle"; 2,266,770 to Harlow entitled "Turbomachine Rotor Assembly"; 3,610,778 to Schottikon entitled "Support For Rotor Blades In A Rotor"; 3,666,376 to Damlis entitled "Turbine Blade Damper"; 3,709,631 to Karstensen et al entitled "Turbine Blade Seal Arrangement"; 3,751,183 to Nichols et al entitled "Interblade Baffle And Damper"; 3,887,298 to Hess et al entitled "Apparatus For Sealing Turbine Blade Damper Cavities"; 4,182,598 to Nelson entitled "Turbine Blade Damper"; and British Pat. No. 1,259,750 entitled "Rotor For A Fluid Flow Machine" are representative of the substantial attempts to solve rotor blade vibration problems in the past.
Each of the structures described in the above patents is of the blade to blade type configuration in which the damper under centrifugal loads is urged outwardly against the platforms of two adjacent blades. Each of the dampers extends axially across the disk or drum in the cavity beneath the blade platforms.
As will become apparent in the specification which follows, the concepts of the present invention depart both structurally and functionally from those previously utilized in the industry.